1. Field of the Invention
The present invention relates to the fields of wireless communications and antenna architecture and design, and, in particular, to adaptive smart antenna system architectures and designs. More specifically, but without limitation thereto, the present invention aims to create an antenna receiver system that is capable of forming multiple orthogonal beams and differentiating multiple received signals by eliminating signal components whose phase information or other characteristics are known or can be acquired.
2. Description of Related Art
In the field of wireless communications, antennas are widely used to transmit or receive data in the form of radio frequency signals from one place to another. Antennas are used in fields such as satellite, radio, television broadcasting, and cellular phone communications, among other things. These antennas can come in all shapes and sizes, ranging from traditional dish antennas, to antenna arrays that utilize multiple elements.
The performance of an antenna is degraded by the presence of an interfering signal, which can be defined as a signal originating from a source external to the desired signal path that produces undesired artifacts in the signal. This can be intentional interference, such as a jamming signal, or unintentional interference, such as receiving signals from a nearby satellite that is being broadcast on the same frequency. Additionally, when the strength of the interfering signal is too strong the communication quality becomes too low to maintain proper service.
Interference due to signal transmission on same frequencies can pose a problem for ground terminals attempting to transmit or receive signals from a desired source, such as a satellite. Several schemes have been designed to distinguish between signals. For example, digital and analog filters which may be easily implemented to differentiate received signals with different frequencies are widely used today. However, these systems do not present an adequate solution when the frequency of interfering signals are the same or very close to the desired signal.
One possible solution to overlapping frequency use is to use smart antennas equipped with digital beam forming (DBF) techniques to distinguish between signals originating from different directions by forming an orthogonal beam in the direction of the desired signal, while simultaneously forming a null at the direction of interfering sources. This provides an adequate solution to frequency use overlap as the antenna only picks up signals from the desired direction. While DBF techniques solve the issue of multi-directional, multi-signal interference, these smart antennas do not adequately solve the issue of multiple signal, differing strength signals being broadcast from relatively close directions.
The present invention takes advantage of the difference of signal strengths, corresponding directional information and other signal characteristics to calculate the phase information of unwanted signals and eliminate them using an adaptive algorithm. Different from other smart antennas utilizing beam-forming techniques, this invention focuses on eliminating unwanted signal components by adaptively minimizing the correlation between a desired signal and any unwanted components.